Deflection devices of the type mentioned above are used as tensioning devices in anti-skid chains, in particular, in snow chains, in order to tighten the anti-skid chain when fitted. In order to prevent any undesirable loosening of the tensioning chain, movement (rotation) of the deflection roller contrary to the tightening direction is blocked. However, it should be made possible to release such blocking, if required, for example when the chain is to be removed.
AT 408 635 B describes a method of locking a roller in the context of a tightening device for a rope, which is wound up therein, said tightening device comprising an actuation member having three positions. Two ratchet wheels that are connected to one another in a rotationally fixed manner are each assigned to locking pawls and have blocking directions that are opposed to one another. The actuation member acts on the two locking pawls, the first locking pawl engaging in the ratchet wheel assigned thereto in a first locking position of the actuation member, while the second locking pawl engages the ratchet wheel assigned thereto in the second locking position, so as to release the movement of the ratchet wheel in, or contrary to, the tightening direction and to block any movement in, or contrary to, the opposite direction respectively. The actuation member has a third position, a releasing position that can be placed between the first and the second locking positions, in which neither of the locking pawls engages the ratchet wheels assigned thereto and blocking is canceled. In addition to having the two ratchet wheels, this device is complex and makes high demands on the precision of the design. Furthermore, operation of the device involving three possible positions of the actuation member is complicated.